Structural characterization of epitaxial YBCO thin films prepared by a fluorine-free sol–gel method for coated conductors

Using a fluorine-free sol–gel method, both c- and a-axis textured YBCO thin films were synthesized in low oxygen partial pressure. The experimental results of both x-ray diffraction 2θ scan and pole figure showed well epitaxial grown films on LaAlO₃ (LAO) single crystal substrates. When the processing condition was altered, the scanning electron microscopy indicated a large fraction of a-axis oriented grains in the film. High-resolution transmission electron microscopy was performed on both types of films and revealed interface lattice structural characteristics. A classic nucleation and growth model was used to explain the texturing mechanism. Other possible mechanisms for the a-axis oriented grains are also discussed.